3.1 Why doesn't this code:
a[i] = i++;work?
3.2 Under my compiler, the code
int i = 7;
printf("%d\n", i++ * i++);
prints 49.
Regardless of the order of evaluation, shouldn't it print 56?
3.3 I've experimented with the code
int i = 3; i = i++;on several compilers. Some gave i the value 3, and some gave 4. Which compiler is correct?
3.3b Here's a slick expression:
a ^= b ^= a ^= bIt swaps a and b without using a temporary.
3.4 Can I use explicit parentheses to force the order of evaluation I want, and control these side effects? Even if I don't, doesn't precedence dictate it?
3.5
But what about the
&&
and
||
operators?
I see code like
``while((c = getchar()) != EOF && c != '\n')'' ...
3.6 Is it safe to assume that the right-hand side of the && and || operators won't be evaluated if the left-hand side determines the outcome?
3.7 Why did
printf("%d %d", f1(), f2());
call f2 first?
I thought the comma operator guaranteed left-to-right evaluation.
3.8 How can I understand complex expressions like the ones in this section, and avoid writing undefined ones? What's a ``sequence point''?
3.9 So if I write
a[i] = i++;and I don't care which cell of a[] gets written to, the code is fine, and i gets incremented by one, right?
3.10a People keep saying that the behavior of i = i++ is undefined, but I just tried it on an ANSI-conforming compiler, and got the results I expected.
3.10b People told me that if I evaluated an undefined expression, or accessed an uninitialized variable, I'd get a random, garbage value. But I tried it, and got zero. What's up with that?
3.11 How can I avoid these undefined evaluation order difficulties if I don't feel like learning the complicated rules?
3.12a What's the difference between ++i and i++?
3.12b If I'm not using the value of the expression, should I use ++i or i++ to increment a variable?
3.13 I need to check whether one number lies between two others. Why doesn't
if(a < b < c)work?
3.14 Why doesn't the code
int a = 1000, b = 1000; long int c = a * b;work?
3.14b How can I ensure that integer arithmetic doesn't overflow?
3.15 Why does the code
double degC, degF; degC = 5 / 9 * (degF - 32);keep giving me 0?
3.16 I have a complicated expression which I have to assign to one of two variables, depending on a condition. Can I use code like this?
((condition) ? a : b) = complicated_expression;
3.17 I have some code containing expressions like
a ? b = c : dand some compilers are accepting it but some are not.
3.18 What does the warning ``semantics of `>' change in ANSI C'' mean?
3.19 What's the difference between the ``unsigned preserving'' and ``value preserving'' rules?
about this FAQ list
about eskimo
search
feedback
copyright
Hosted by
